Summary of Work: This project will explore the complexity of mismatch repair in higher cells. Specifically, we are interested in elucidating the roles of MSH4 and MSH5 in recombination and any possible redundancy in DNA repair. Recent studies from Paquis-Flucklinger and others have shown yMLH1, known to be involved in mismatch repair (human homologue implicated in HNPCC kindreds) interacts with yMSH4. Since MSH4 expression is highest during early meiosis and therfore not detectable during vegetative growth and that MLH1 is not expressed during this time suggests yMLH1 is recruited by the MutS-II like gene in promoting meiosis-specific reciprocal recombination. In addition, that yMSH4 and yMSH5 appear to interact, suggests these MutS-II like genes act in concert i.e. as a heterodimer during meiosis. Current models of recombination and mismatch repair suggest that branch migration is mediated by components of mismatch repair when markers are selected in the vicinity of sequence divergence. Now it appears in higher cells that, components of mismatch repair play a direct role in stabilizing DNA crossovers. Hence, we would like to established in more detail the biochemistry (DNA specificity) of yMSH4,5 and what redundancies in roles that might exists with yMSH2 in meiosis. Currently we have amplified out Saccharomyces cerevisiae MSH4 from the chromosomal DNA along with obtaining the MSH5 plasmid. MSH5 has been fused to the gal 10 promoter so as to allow coexpression of both MSH4 & MSH5.